Epsilon Archive for Student Projects

Abstract

During the 1800´s and 1900´s, Swedish rivers were heavily modified to support log driving, this led to significant decrease of ecological function and integrity in the river systems. In recent time, restoration has become an important tool to recover the ecological status, especially following the acceptance of the EU Water Framework Directive. This study analyses the short-term effects of restoration measures implemented on the ReBorN LIFE project on brown trout and salmon in Lögdeälven. Using electrofishing data from 11 different survey sites dating back to the year 2000 and up until 2024, I analyse trout and salmon densities, before and after restoration using linear mixed models and trend plots. No significant difference were observed between the before- and after period on either salmon or trout. The trends indicate a decline in densities in both species, trout with a negative trend from the start (year 2000), and salmon with a positive trend before restoration but a negative trend after. Several factors may influence the result both in trend and in lack of significance, for example, disease, river broadening, environmental factors, and changes in electrofishing gear. It is possible that the short time-period of post restoration monitoring is not enough to capture the restoration effects. This study points towards the need for long term monitoring, and potentially new assessment methods to accurately study the full effects of restoration on fish populations.